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I am using the Tektronics TDS 7404 Digital Phosphor Oscilloscope.
I am using it to measure phase shift between a digital signal
on Channel1 to a digital signal on Channel2.

I am using the "delay" measure on the scope to calculate this delta.
Q1: Can you tell me please how the "delay" function is defined?

I am finding that both rising edge on Channel1 and the rising
edge on Channel2 must be visible on the screen for the delay
to be captured. If the rising edge of Channel2 is off the screen
a "?" mark is printed to the screen.

For small periods and phases this is fine, as the resolution
will be good. However for large periods, and large phase shifts, I
fear that accuracy is
lost when I increase the time base to have both edges in the same
screen.

Q2 Is there a way around this problem?

Q3 Is their another function that I can use to measure phases where I
am not limited by the screen size?

Further details:
The design that I am testing allows one to configure a known
delay between these edges. In this way every rising edge on Channel2
is always offset from its corresponding edge on Channel1 by a certain
phase shift. Both channels are at the same period, so there is a one-
to-one correspondence between rising edges.

Regards
PS

[Scott Dorsey]

wrote:
I am using the Tektronics TDS 7404 Digital Phosphor Oscilloscope.
I am using it to measure phase shift between a digital signal
on Channel1 to a digital signal on Channel2.

I am using the "delay" measure on the scope to calculate this delta.
Q1: Can you tell me please how the "delay" function is defined?

The manual for the Tek scope will tell you. If you spell it properly,
you should be able to find a manual on tektronix.com. There is a way to
set it up for several different units.

However, you should know that lissajous method is MUCH more accurate
for determining small delays.

I am finding that both rising edge on Channel1 and the rising
edge on Channel2 must be visible on the screen for the delay
to be captured. If the rising edge of Channel2 is off the screen
a "?" mark is printed to the screen.

For small periods and phases this is fine, as the resolution
will be good. However for large periods, and large phase shifts, I
fear that accuracy is
lost when I increase the time base to have both edges in the same
screen.

Welcome to the marvelous world of digital scopes.

Q2 Is there a way around this problem?

Use an analogue scope with a storage tube?

Q3 Is their another function that I can use to measure phases where I
am not limited by the screen size?

You're not measuring phase, you're measuring delay.

Further details:
The design that I am testing allows one to configure a known
delay between these edges. In this way every rising edge on Channel2
is always offset from its corresponding edge on Channel1 by a certain
phase shift. Both channels are at the same period, so there is a one-
to-one correspondence between rising edges.

What sort of delays are we talking about here? Nanoseconds? Minutes?
What sort of signal bandwidth? Is delay too long and the lowest frequency
of the passband too high to use lissajous method?
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."